Reticular endings of Purkinje cell axons in the rat cerebellar nuclei: scanning electron microscopic observation of the pericellular plexus of Cajal.

The pericellular plexus of Purkinje cell axons in the cerebellar nuclei was first recorded by Cajal (1911), using the Golgi method. The present study observed the axonal plexus in the rat by scanning electron microscopy after the plexus' detachment from the soma of target neurons by NaOH maceration. The pericellular plexus revealed numerous axons with ellipsoidal and moniliform swellings. They branched and crossed with each other to form, as a whole, a reticulum which enveloped the target neuron instead of multiple isolated boutons. Some axon terminals were separated from each other by thin glial processes, while others lacked such septa, thus being directly juxtaposed. Immunohistochemistry for spot 35 protein, a Purkinje cell-specific protein, detected similar beaded and reticular axons terminating on the neuronal somata, confirming their identification as Purkinje cells. Transmission electron microscopic observation showed that most of the axon terminals in question contained elliptical vesicles, characteristic for Purkinje cells. The vesicles were not accumulated toward small patchy areas of synaptic specialization but disseminated along the entire length of the terminal portion of axons.